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The first step towards extracting a high-quality olive oil begins with the harvest. A decisive factor in this respect is ensuring that the fruit is harvested at exactly the right time. Olives have the optimum ripeness and maximum oil content when their colour changes from green to black. It is also necessary to harvest the olives as gently as possible, i.e. with as little damage as possible, and then to clean them thoroughly. If the skin of the olive is damaged, an unwanted oxidation process begins.
Harvesting using a vibrating rake is just as gentle as hand-picking. This method saves a considerable amount of time, thus permitting the valuable fruits to be processed more quickly. Olives should, wherever possible, be processed within 24 hours of harvesting so that they do not begin to decay.
After being transported to the oil mill the fruits are pressed between grinding stones to form a paste of flesh, kernel, oil and water. The oil may now be extracted in two ways – using a press or a centrifuge.
If the oil is to be pressed, the paste is spread out on nets or mats (capochos) in rural areas. These are then stacked on top of one another and the liquid slowly presses itself out thanks to its own weight. In the wake of increasing automation hydraulic presses are now also used for this process.
After the pressing stage, use is made of the physical phenomenon that oil is lighter than water and thus floats on the surface and may be easily decanted.
Centrifugation is gentler and is now used for ca. 80% of all oil extraction. The paste is placed in horizontal decanters where the solids separate from the liquid. A vertical decanter separates the liquid into olive oil and the water contained in the fruit. With the aid of this method it is possible to extract more oil in a shorter period of time, thus allowing the time the olives are stored to be shortened. The fruits are processed in a fresher state.
Following this initial filtration the olive oil is bottled in a naturally cloudy state or, if desired, it may be filtered again. The quality of the oil does not change with further filtering; it is merely a question of personal taste whether a clear or naturally cloudy olive oil is preferred.
By the way:
As the temperature during the entire oil extraction process never rises above 30 degrees centigrade, oil extracted in this manner is known as "cold-pressed oil". In contrast to many other cold-pressed oils, thanks to its special composition olive oil can not only be used for cold dishes but also for cooking and baking.
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